In phased arrays of antennas, the relative phases of the signals feeding the antennas are varied so that the effective radiation pattern of the array is enhanced in a desired region and suppressed in undesired directions. Phased-array technology was originally developed for radar systems, but has since also been used, for example, in radio astronomy, radio broadcasting, optical communication, sonar (sound navigation and ranging) systems, and loudspeaker systems for entertainment. In sound applications, phased arrays are often referred to as beamformers.
Beamforming techniques have supplemented the traditional functions of loudspeaker systems—sound amplification and reproduction with a given level of clarity and intelligibility—with the capability of containing sound waves in a beam aimed at one or more particular points or listeners. This capability enables providing sound at a desirable volume level to a target person, while keeping the volume in the surrounding area below (or at least not significantly above) the audible level, so as to avoid disturbing others. Acoustic beamforming can also be used to provide different audio stimuli to different people occupying the same room, e.g., a museum or lecture hall. Moreover, it can be employed to create more realistic stereo effects without the need for headphones, or more complex directional sound, for example, in home entertainment audio systems.
Existing audio beamforming systems suffer from a number of deficiencies and conflicting goals. Most notably, the effectiveness and precision of beamforming depends on the number of independently addressable speakers, and therefore, of system complexity. Usually, the greater the number of speakers and amplifiers, the better beamforming capabilities will be. The feasibility of complex systems, however, is subject to technical and economic constraints. The directionality of acoustic beams is further dependent on the frequency range of the signal. Low-frequency components are less directional than higher-frequency components, thereby impacting sound fidelity.
Accordingly, there is a need for speaker systems and sound-reproducing methods which achieve high-fidelity beamforming without unduly increasing system complexity.